1. Field of the Invention
This invention relates to a multi-step process for purifying wastewater containing organic and color-causing pollutants and more particularly to such processes including a biophysical treatment first stage, an oxidizer treatment second stage and an adsorbent contact treatment third stage.
2. Information Disclosure Statement
Wastewaters generated in the production and use of organic-based dyes present a most difficult treatment problem. These wastewaters contain organic substances which may be measured by the pollutant parameter chemical oxygen demand (COD). These organic substances render the wastewaters highly colored which makes them aesthetically unacceptable. The organic components are difficult to remove with adsorbents and are resistant to biological degradation as well. Treatment which removes the major portion of the organic substances, as measured by COD, may still result in a highly colored effluent. Applicants have discovered a unique and economical process to effectively treat these difficult wastewaters.
A particularly useful process for removing pollutants from wastewater employs a mixture of bacteria and powdered activated carbon in a treatment zone. This process, called the PACT.RTM. treatment system, is disclosed by Hutton et al. in U.S. Pat. Nos. 3,904,518 and 4,069,148. The PACT treatment system operates as a continuous flow process with an aeration basin followed by a separate clarifier to separate biologically active solids and carbon from the treated wastewater, and the settled sludge is returned to the aeration basin.
Copa et al. in U.S. Pat. Nos. 4,810,386 and 4,897,196 disclose two-stage biophysical treatment systems for treatment of wastewaters. One operates in a continuous flow mode while the other operates in a batch mode. Complete settling of biophysical solids in the first stage is not required since the adsorbent contact second stage captures carried over solids.
Rose, in U.S. Pat. No. 4,851,128, discloses a process for decolorizing pulp mill wastewaters which contain color bodies. The wastewater is contacted with a carbon adsorbent which adsorbs the color bodies. After a time, the adsorbent is removed from use and heat treated to pyrolyze the adsorbed color bodies and regenerate the adsorbent for reuse. The wastewater may be preconditioned with a small amount of cationic flocculent to improve color removal.
Kamke, in U.S. Pat. No. 5,075,015 describes control of the color of a treatment system by removing color and oxidizable organic matter from thermally conditioned sludge liquor by treating the liquor with low dosage (250 to 430 mg/l) of chlorine which removes 20 to 70 percent of the color and produces a chlorine residual in the liquor.
Copa et al. in U.S. Pat. No. 4,919,815 disclose a two-stage process, including a biophysical anaerobic treatment stage followed by a biophysical aerobic treatment stage, for COD containing wastewaters.